American light-welterweight boxer Brandon Lee Ríos, the former WBA lightweight champion, has denied taking any illegal substances after he was suspended by the Macau Commission for testing positive for a banned substance following his November 23 loss to Manny Pacquiao in Macau.

Rios lost a wide unanimous decision to Pacquiao in the welterweight bout and it is believed that he tested positive for dimenthylamylamine in his post-fight urinalysis. Rios and Pacquiao were randomly tested by the Voluntary Anti-Doping Association (VADA). While Pacquiao passed all tests given by VADA, Rios managed to pass the first four but failed the final test.

Dimenthylamylamine, commonly known as DMAA, is a stimulant banned by both VADA and the World Anti-Doping Agency. Classified as a performance enhancing drug, DMAA is found in the over-the-counter fitness supplement Jack3d, which Rios admitted to using many years ago when he started his career. He later remarked his trainer, Robert Garcia, told him it was not required and he stopped using it and had never taken it again.

The Food & Drug Administration in April this year warned consumers about taking DMAA and said it is most commonly used in supplements promising weight loss, muscle building and performance enhancement; it can elevate blood pressure and could lead to cardiovascular problems, including heart attack, shortness of breath and tightening of the chest.

Brandon Rios claimed that he never took anything banned and said he asked questions of conditioning coach Alex Ariza before ingesting anything he did not know. Rios remarked he is not a dirty fighter and if they want to test me 24-7, day and night, they could test me all they want as he knows that he don't take no steroids. Rios added that he doesn't take any diet supplements like that and said he takes punch very well. He went on to add that this is the first time he had lost weight the right way and he followed a diet plan and had an actual nutritionist.

Rios said he passed all of those other tests and all of a sudden, the last time, the last one, after we had that incident, then that's when we tested positive. When asked of Team Pacquiao had something to do with the positive test, Brandon Rios said he is not going to sit here and point and blame anybody but remarked he did found it odd the positive test came after the incident. Rios was referring to a recent incident between Alex Ariza, his conditioning coach, and Pacquiao trainer Freddie Roach.

Top Rank promoter Bob Arum said he can say unequivocally that it was not a steroid-related substance and it was some substance that was like a minor kind of thing that you're not supposed to take, something you take for weight loss, like a diuretic. He added they say it's not a steroid but it was something you should not have in your urine after a fight. Alex Ariza, Rios' strength and conditioning coach, was blamed by Arum for the failed test and said it is not the fighter's fault and it's the people who are conditioning him. He added Rios is following orders on what to eat and drink, so he doesn't blame him.